Hello, I was wondering if anyone remembers on the early xr's and the later xl's the strange decompression chamber that could be accessed on one side of the head via allen bolts and a side panel. Well, I just rebuilt an XL600R, I got it started for the first time, (I didn't have the secondary decompression line which runs from the head down to a lever arm by the kick start) I rode it around the block one time and I was cruising along a low rpms when I saw the paint on decompression chamber melt followed quickly by the aluminum melting their and the engine loosing all its compression. I am completely lost as to what happened. What is this chamber for? What might have caused the this tremendous exhaust pressure to buid up their? THank YOu, I appreciate any incite.